*{
    margin: 0;
    padding: 0;
    box-sizing: border-box;
}
*::after{
    box-sizing: border-box;
}
*::before{
    box-sizing: border-box;
}
#demo{
    word-break: break-all;
}
#div1{
    position: fixed;
    left: 50%;
    transform: translateX(-50%);
    top: 20px;
}
#div1::before{
    content: '';
    display: block;
    position: absolute;
}
#div1::after{
    content: '';
    display: block;
    position: absolute;
}
@media (max-width: 500px){
    #html{
        height: 60vh;
        overflow: hidden;
    }
    #div1Wrapper{
        height: 40vh;
    }
    #div1{
        position: relative;
        bottom: 0;
        left: 50%;
        transform: translateX(-50%);
    }
}